There are conventionally known, as developing devices for developing an electrostatic latent image on a photosensitive member as an image carrying member, those adopting a one-component development method and those adopting a two-component development method. A two-component development method uses developer containing toner and magnetic carrier; this provides a stabile amount of electrostatic charge for a long period, and is suitable to obtain long service lives. For example, in a developing device adopting a two-component development method, developer containing toner and magnetic carrier is stored, and the developer is fed from a stirring member to a developing roller (developer carrying member). The developing roller has a magnet (such as a regulating pole) inside it, and by the action of this magnet (such as a regulating pole), developer is carried in the form of a magnetic brush on the surface of the developing roller. As the developing roller rotates, the developer is transported to a part of the developing roller opposite the photosensitive member. Then, out of the developer, only toner is fed to the photosensitive member, and thereby an electrostatic latent image on the photosensitive member is turned into a visible image as a toner image.
There is also known a developing device comprising a regulating member for regulating the layer thickness of developer to make constant the amount of developer that, as a developing roller rotates, is transported to a part thereof opposite a photosensitive member and a magnet arranged on the upstream side of the regulating member with respect to the rotation direction of the developing roller. As such a developing device, a developing device is known that uses a one-component developer containing magnetic toner (e.g., Patent Document 1 identified below). In this developing device, a magnet is arranged on the upstream side of a regulating member with respect to the rotation direction of a developing roller so that, at a tip part (a developing roller side tip part) of the regulating member, a magnetic pole of the polarity opposite to that of a regulating pole is induced, and thereby the developer passing between the developing roller and the regulating member is regulated to have a predetermined layer thickness.